C 5 Pentacle Structures: A Localization-Delocalization Matrices Approach.

This article explores the possible presence of a pentacle valence bond structure in C 5 ${_5 }$ cyclic molecules. At this end, we have used quantum chemistry tools to elucidate the possible arrangement and the nature of chemical bonds within linear, cyclic, and three-dimensional structures only formed by five carbon atoms. While the linear structure is clearly the most stable one, local minima were obtained for both bi- and three-dimensional structures. Using the localization-delocalization matrices approach, we characterize both the minimum linear structure and the cyclic ones. Interestingly, the linear structure is a combination of ionic and covalent bonds, albeit the four distances are almost identical, when using Density Functional Theory. For cyclic C 5 ${_5 }$ , the pentacle bonding arrangement emerges as a significant Lewis structure, indicative of an unusual formal configuration characterized by five intersecting C-C bonds. Our calculations show that this pentacle arrangement in cyclic C 5 ${_5 }$ scheme is also present in the more known cyclo-pentadienyl molecule.